The present invention concerns laser micromachining and, in particular, using laser pulses to form a microcavity array in a metal foil.
Incandescent light sources rely on the emission of radiation by a hot material. Incandescent light sources, such as a filament of a conventional light bulb, emit only a relatively small portion of their energy in the form of visible light. Most of the remainder of the emitted energy is in the infrared region of the spectrum. In addition, the filament emits light in all directions.
One method for reducing the infrared emissions on an incandescent light source is to use an optical microcavity, as described in U.S. Pat. No. 5,955,839 entitled INCANDESCENT MICROCAVITY LIGHTSOURCE HAVING FILAMENT SPACED FROM REFLECTOR AT NODE OF WAVE EMITTED. In this patent, conventional microelectronic processing techniques are used to form a filament in a single optical microcavity. As described in this patent, the presence of the optical microcavity provides greater control of the directionality of emissions and increases the emission efficiency in given bandwidth (i.e. the 1-2 xcexcm near infrared band).
The same type of efficiency gain may be obtained by forming an array of microcavity holes in an incandescent light source. Such a light source may, for example, have microcavities of between 1 xcexcm and 10 xcexcm in diameter. While features having these dimensions may be formed in some materials using standard microelectronic processing techniques, it is difficult to form them in metals such as tungsten that are commonly used as incandescent filaments.
The present invention is embodied in a method and apparatus for forming an array of microcavities on the surface of a workpiece. The apparatus includes a laser which produces a beam of laser light pulses, a device that divides the beam into multiple beams and a lens system that focuses the multiple beams onto the workpiece.
According to one aspect of the invention, the apparatus operates by generating multiple beams of laser pulses of a first diameter and then magnifying the pulses by a magnification factor less than 1 before applying the magnified beams of laser pulses to the workpiece.
According to another aspect of the invention, the laser is an excimer laser;
According to yet another aspect of the invention, the laser is an ultrashort pulse laser;
According to another aspect of the invention, the beam dividing device is an opaque mask having a pattern of openings.
According to a further aspect of the invention the beam dividing device is a diffractive optical element.
According to yet another aspect of the invention, the apparatus includes a quarter wave plate that converts the beam of laser light pulses into a beam of circularly polarized pulses.
According to a further aspect of the invention, the apparatus includes a device that homogenizes the intensity of the laser light pulses before they are applied to the workpiece.